A variety of apparatuses and techniques have heretofore been used or proposed for use to effect a microcasting or atomization of molten metals and metal alloys into metal powders of the required purity and particle size, rendering them suitable for use in the fabrication of various components employing conventional powder metallurgical techniques. Such prior art techniques include liquid atomization, gas atomization, as well as centrifugal spin microcasting techniques to fragmentize molten metals into droplets, which upon solidification can be recovered and screened to provide metal powders of the desired particle size range.
Typical of a liquid atomization apparatus particularly suitable for making copper and copper-lead alloy powders is that disclosed in U.S. Pat. No. 2,460,993, granted to Gordon J. LeBrasse et al. on Feb. 8, 1949, entitled "Apparatus for Atomizing Metal". Similarly, gas atomization apparatuses typical of those heretofore employed are disclosed in U.S. Pat. No. 2,968,062, granted to Robert L. Probst et al. on Jan. 17, 1961, for "Atomizing Nozzle and Pouring Cup Assembly for the Manufacture of Metal Powders", and U.S. Pat. No. 3,253,783, granted to Robert L. Probst et al. on May 31, 1966, for "Atomizing Nozzle". The devices and techniques as disclosed in the aforementioned United States patents, which are assigned to the same assignee as the present invention, have provided a satisfactory means for producing metal and metal alloy powders of the desired size and degree of purity at commercially acceptable costs. In the atomization of superalloys where metal powders of extremely high purity are required, it is usually necessary to employ inert gases to avoid oxidation attack of the reactive alloy elements therein such as titanium and/or aluminum, whereby the resultant powder contains less than about 100 parts per million (ppm) oxygen, rendering such powders eminently suitable for the fabrication of components having excellent high temperature mechanical properties, such as required in the rotating components in the hot section of aircraft gas turbine engines and the like.
Some problems have been encountered in controlling the fluid atomization process so as to provide a high yield of a metal powder product of the desired size range without producing excessive quantities of unuseable fines and larger irregular-shaped particles that must be recycled. For these and other reasons, there has been a continuing need for an improved technique for producing metal powders which are of high purity and wherein the microcasting can be controlled so as to maximize the yield of powder product having the desired particle size range and configuration.
The process of the present invention provides an improved technique for microcasting metals and metal alloys and can be practiced in an environment substantially devoid of any contaminating substances, such as in a substantial vacuum, and further enables careful control of the fragmentation process to achieve improved yields of metal powder of the desired particle size range.